The present invention relates generally to current sensing devices for electrical systems, and more particularly to resettable alternating current fault indicators.
Various types of self-powered fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the systems and derive their operating power from inductive coupling to the monitored conductor, and test point type fault indicators, which are mounted over test points on cables or associated connectors of the systems and derive their operating power from capacitive coupling to the monitored conductor. Such fault indicators may be either of the manually reset type, wherein it is necessary that the indicators be physically reset, or of the self-resetting type, wherein the indicators are reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E. O. Schweitzer Manufacturing Company of Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740, 3,906,477, 4,063,171, 4,234,847, 4,375,617, 4,438,403, 4,456,873, 4,458,198, 4,495,489, 4, 4,974,329, and 5,677,678 of the present inventor.
Detection of fault currents in fault indicators is typically accomplished by means of magnetic switch means such as a magnetic reed switch in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the magnetic switch actuates a trip circuit which produces current flow in a trip winding to position an indicator flag visible from the exterior of the indicator to a trip or fault indicating position. Upon restoration of current in the conductor, a reset circuit is actuated to produce current flow in a reset winding to reposition the target indicator to a reset or non-fault indicating position.
In certain applications the need arises for indicating or recording the detection of a fault current at a location remote from the fault indicator. For example, where fault indicators are installed in each of multiple distribution circuits fed from a common source, it may be desirable to monitor the fault indicators at a central monitoring facility to enable a fault to be quickly isolated. Repair crews can then be efficiently designated to the known location of the fault.
Because of the compact construction and limited power available in self-powered fault indicators it is preferable that the auxiliary contacts require minimal additional circuitry and structure within the fault indicator while providing reliable contact closure upon occurrence of a fault. The present invention is directed to a novel contact arrangement which meets the above requirements by utilizing a magnetic winding, such as the actuator winding of the electro-mechanical indicator flag assembly typically utilized in fault indicators, in conjunction with a magnetic circuit to actuate a magnetically biased reed switch to provide contact actuation upon occurrence of a fault.
Accordingly, it is a general object of the present invention to provide a new and improved fault indicator having auxiliary contacts for signaling fault occurrence.
It is a more specific object of the present invention to provide a new and improved self-powered fault indicator which provides contact closure upon occurrence of a fault current in a monitored conductor.
It is a still more specific object of the present invention to provide a fault indicator wherein a fault-indicative contact closure is provided utilizing the electro-magnetic flag indicator assembly of the fault indicator.